Stud for fastening the outer end of a hair spring for a timepiece



March 3, 1964 ER 3,122,880

STUD FOR FASTENING TI-IE OUTER END OF A HAIR SPRING FOR A TIMEPIECE Filed Sept. 1'7, 1962 INVENTOR RUDOLF GREINER ATTORNEY United States Patent 3,122,880 STUD FOR FASTENING THE OUTER END OF A HAIR SPRING FOR A TIMEPIECE Rudolf Greiner, Langenthal, Switzerland, assignor to Greiner Electronic A.G., Langenthal, Switzerland, a corporation of Switzerland Filed Sept. 17, 1962, Ser. No. 224,006 Claims priority, application Switzerland Dec. 19, 1961 3 Claims. (Cl. 58-115) This invention relates to a stud for fastening the outer end of a hair spring for a time piece.

An object of the invention is a stud of the kind outlined having a cylindrical head portion provided with a transverse groove which, in the longitudinal direction of the stud, has a base longer than the blade width of the hair spring to be fastened to said stud, said head portion having a recess penetrating from the end of said head portion in the longitudinal direction of the stud in such a way that the hair spring tangentially inserted in said groove may be secured by deformation of said head in the longitudinal direction of the stud. Another object of the invention is a stud of the kind mentioned above wherein said groove is an annular groove of dovetail section and said recess is a cylindrical bore penetrating in said stud in its longitudinal direction up to the region of said transverse annular groove in such a way that a narrow annular neck remains which connects the peg circumscribed by the base of said annular groove with the remaining ringshaped part of the head portion of said stud. In order to fasten the end of said tangentially inserted hair spring in said stud the head portion of the stud is depressed, simultaneously shearing off said annular neck and at least partially pressing said remaining ring-shaped part onto said peg until the hair spring is secured between said ring-shaped part and the remaining transverse surface of said annular groove.

These and other objects and the advantages of the invention will best be understood from the following description of a specific embodiment when read in connection with the accompanying drawing in which:

FIG. 1 is a view of the stud before secured to the hair spring,

FIG. 2 is a view of the stud with the end of a hair spring inserted in its transverse groove and with its head portion deformed in order to fasten the hair spring in the stud, and

FIG. 3 is a plan view, corresponding to FIG. 2, of the deformed head portion of the stud and of the hair spring fastened therein.

In FIGS. 1 and 2 the stud is shown partly in section.

The stud 4 substantially comprises a piece of round rod, one end of which has a transverse groove 5 which for technical reasons is preferably annular. In FIG. 1 the annular groove 5 is of dovetail cross-section throughout. The base 6 of the groove 5 circumscribes a peg 7 which is smaller in diameter than the adjoining cylindrical parts of the stud 4. Sunk into the grooved head from the outer end thereof and extending longitudinally is a recess 8 which extends axially up to the annular groove 5. The recess is preferably in the form of a cylindrical bore with a maximum diameter equal to the external diameter of the peg 7. In FIG. 1 the depth of the recess 8 is chosen so that the head forms a ring 9 protruding longitudinally of the peg 7 and connected to the peg 7 by a narrow neck 10.

The end of the hair spring 11 is inserted tangentially in the groove 5 as shown in F168. 2 and 3. The diameter of the peg 7 is so chosen that the depth of the groove 5, measured radially, is approximately three to four times 3,122,880 Patented Mar. 3, 1964 the thickness of the blade of the hair spring 11 to be fastened. The dimension of the base 6 of the groove 5 longitudinally of the stud should preferably be about twice the blade width of the hair spring 11. Comparison of FIGS. 1 to 3 shows the principle of such dimensioning. In order to fasten the end of the hair spring 11 lying tangentially against the base 6 of the groove 5, pressure is exerted on the ring-shaped part 9 in the longitudinal direction of the stud 4 until the annular neck 10 is sheared off and the peg 7 penetrates into the recess 8. The part 9 is finally pressed down longitudinally of the stud 4 onto the peg 7 until the inserted end of the hair spring is secured between the part 9 and the remaining bearing surface 12 of the groove 5. As the hair spring 11 is generally made of a harder material than the stud 4, the shaped surface 12 of the stud 4 and the shaped surface 13 of the part 9 facing it are each pressed slightly inwardly where the blade of the hair spring leaves the stud. This is illustrated in FIG. 2.

By this method the end of the hair spring 11 is fastened in the stud 4 in a manner which satisfies all practical requirements. The emergence of the hair spring from the stud is quite clearly defined and there is no danger of a hair spring 11 which has been previously adjusted in length being undesirably drawn along when the described fastening is made. As the deformation of the head portion of the stud 4 consists only of shearing off the annular neck 10 and then pressing the part 9 onto the peg 7, the fastening of the hair spring 11 is an extremely simple straightforward operation which can safely be left to less experienced personnel.

Series of semi-automatic production is also possible if the described stud is used. The stud itself is cheap to produce as both the annular groove 5 and the recess 8 can be made on normal automatic rotary machines.

I claim:

1. A stud for fastening the outer end of a hair spring for a timepiece, said stud having a cylindrical head portion provided with a transverse annular groove which, in the longitudinal direction of the stud, has a base longer than the blade Width of the hair spring to be fastened by means of said groove, and said head portion having a cylindrical bore penetrating from the end of said head portion in the longitudinal direction of the stud up to the region of said transverse groove in such a way that a narrow annular neck remains which connects the peg circumscribed by the base of said transverse groove with the remaining ring-shaped part of the head portion of said stud.

2. A stud according to claim 1, in which the diameter of said peg is equal to the diameter of said here.

3. A stud according to claim 1, in which in order to fasten the end of said tangentially inserted hair spring in said stud said head portion is depressed, simultaneously shearing off said annular neck and at least partially pressing said remaining ring-shaped part onto said peg until said hair spring is secured between said ring-shaped part and the remaining transverse surface of said annular groove.

References Cited in the file of this patent UNITED STATES PATENTS 2,191,780 Tinnerman Feb. 27, 1940 2,724,867 Smith, Nov. 29, 1955 2,813,568 Kilmarx Nov. 19, 1957 2,931,164 Schweizer et al Apr. 5, 1960 2,956,468 Macy Oct. 18, 1960 FOREIGN PATENTS 311,287 Switzerland Jan. 31, 1956 

1. A STUD FOR FASTENING THE OUTER END OF A HAIR SPRING FOR A TIMEPIECE, SAID STUD HAVING A CYLINDRICAL HEAD PORTION PROVIDED WITH A TRANSVERSE ANNULAR GROOVE WHICH, IN THE LONGITUDINAL DIRECTION OF THE STUD, HAS A BASE LONGER THAN THE BLADE WIDTH OF THE HAIR SPRING TO BE FASTENED BY MEANS OF SAID GROOVE, AND SAID HEAD PORTION HAVING A CYLINDRICAL BORE PENETRATING FROM THE END OF SAID HEAD 